Grouping-based data transceiving method in wireless lan system and apparatus for supporting same

ABSTRACT

Provided is a data transceiving method performed by a station (STA) in a wireless LAN system. The method comprises: receiving subgrouping parameter information from an access point (AP); determining whether a frame buffered in the STA subgroup in which the STA is contained exists or not based on the subgrouping parameter information; receiving a TIM element in a channel access interval for the STA subgroup from the AP if the buffered frame exists; and exchanging the AP and the frame in the channel access interval based on the TIM element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a station (STA) grouping-based data transceiving methodin a wireless LAN system and an apparatus for supporting the same.

2. Related Art

With the growth of information communication technology, variouswireless communication technologies have been recently developed. Amongothers, Wireless Local Area Network (WLAN) is a technology that allowsfor wireless access to the Internet at home or business or in a specificservice area using a handheld terminal such as a personal digitalassistant (PDA), a laptop computer, a portable multimedia player (PMP),etc.

Unlike an existing wireless LAND system for supporting High Throughput(HT) and High Throughput (VHT) using 20/40/80/160/80+80 MHz bandwidth of2 GHz and/or 5 GHz band, a wireless LAN system capable of being operatedat a band less than 1 GHz is suggested. If the wireless LAN system isoperated at a band less than 1 GHz, a service coverage by an accesspoint AP may be expanded as compared with an existing LAN system.Accordingly, one AP manages more STAs.

If the number of STAs associated with the AP is considerably increased,a problem may occur in a Traffic Indication Map (TIM) protocol being atransceiving protocol for an STA operated in a power save mode and in achannel access operation of the STA. Accordingly, there is a need for amethod where a wireless LAN system in which very many STAs coexistefficiently approaches a channel to transceive data.

SUMMARY OF THE INVENTION

The present invention to solve the above-described problems provides agrouping-based data transceiving method in a wireless area networksystem and an apparatus for supporting the same.

In an aspect, a method for transmitting and receiving data in a wirelesslocal area network system is provided. The method performed by a station(STA) includes receiving subgrouping parameter information from anaccess point (AP), determining whether a frame buffered in a STAsubgroup to which the STA belongs exists based on the subgroupingparameter information, receiving a traffic indication map (TIM) elementin a channel access period for the STA subgroup from the AP if it isdetermined that the buffered frame exists, and exchanging frames withthe AP during the channel access period based on the TIM element.

The subgrouping parameter information may comprise a group ID field toindicate an STA group to which the subgrouping parameter information isapplied.

The method may further include determining whether the STA subgroup towhich the STA belongs is indicated by the group ID field of thesubgrouping parameter information. The STA group may be grouped based onan association identifier (AID) assigned when the STA is associated withthe AP. The step of determining whether a frame buffered in the STAsubgroup exists may be performed when the STA subgroup to which the STAbelongs is indicated by the group ID field.

The subgrouping parameter information may further comprise a subgroupfield to indicate the number of a plurality of STA subgroups included inan STA group indicated by the group ID field, and a subgroup indexbitmap field to indicate whether there are buffered frames with respectto the plurality of STA subgroups, respectively.

The step of determining whether a frame buffered in the STA subgroup towhich the STA belongs exists based on the subgrouping parameterinformation may include determining the STA subgroup of the STA based onthe subgroup field of the subgrouping parameter information, anddetermining whether a buffered frame for the STA subgroup exists or notbased on the subgroup index bitmap field.

The group index bitmap field may comprise a bitmap sequence to indicatewhether groups buffered with respect to the plurality of STA subgroupsincluded in the STA group exist or not, respectively

The TIM element may comprise an STA group ID field to indicate an STAgroup to which the TIM element is applied, a subgroup index field toindicate an STA subgroup of the STA group to which the TIM element isapplied, and a bitmap field to indicate whether there are framesbuffered with respect to STAs of the STA subgroup indicated by thesubgroup index field, respectively.

The step of exchanging the frames with the AP may comprise determiningwhether the TIM element is for the STA subgroup of the STA, determiningwhether the buffered frame for the STA exists or not based the bitmapfield when the TIM element is for the STA subgroup of the STA, andreceiving the buffered frame from the AP within the channel accessperiod when the buffered frame exists.

When an STA group of the STA is the STA group indicated by the group IDfield of the TIM element and the subgroup of the STA is the STA subgroupindicated by the subgroup index field of the TIM element, the TIMelement may be determined for the STA subgroup of the STA.

In another aspect, a station (STA) for operated in a wireless local areanetwork system is provided. The STA includes a transceiver configured totransmit and receive a radio signal, and a processor functionallyconnected with the transceiver and configured to receiving subgroupingparameter information from an access point (AP), determining whether aframe buffered in a STA subgroup to which the STA belongs exists basedon the subgrouping parameter information, receiving a traffic indicationmap (TIM) element in a channel access period for the STA subgroup fromthe AP if it is determined that the buffered frame exists, andexchanging frames with the AP during the channel access period based onthe TIM element.

A station (STA) grouping-based channel access method can perform STAgrouping based on an AID of an STA to group channel access periods asSTA groups so that the channel access periods are assigned to the STAgroups. Each STA group or each STA subgroup may exchange data with theAP during a channel access period assigned to each STA group or each STAsubgroup. Therefore, the wireless LAN system with very many STAs canefficiently exchange data per STA group.

A Traffic Indication Map (TIM) protocol based data can be transmittedand received based on STA grouping. TIM element based data transmissionand reception can be efficiently provided by reducing an overhead of theTIM element. Since STAs of an STA group and/or an STA subgroup access achannel during a corresponding channel access period to requesttransmission of a buffered frame to the AP, efficiency of channelapproach is increased as compared with the related art so that athroughput rate of data can be improved. Further, since remaining STAsare not unnecessarily operated in an awake state, power save efficiencycan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating the configuration of a general WirelessLocal Area Network (WLAN) system to which an embodiment of the presentinvention may apply.

FIG. 2 is a view illustrating an example of power management operation.

FIG. 3 is a block diagram illustrating an example of a TIM elementformat.

FIG. 4 is a view illustrating an example of a bitmap control field and apartial virtual bitmap field according to an embodiment of the presentinvention.

FIG. 5 is a flowchart illustrating an example of an AP's respondingprocedure in a TIM protocol.

FIG. 6 is a flowchart illustrating another example of an AP's respondingprocedure in a TIM protocol.

FIG. 7 is a flowchart illustrating a procedure of a TIM protocol by aDTIM.

FIG. 8 is a diagram illustrating a signaling procedure to establish TDLSdirect link.

FIG. 9 is a diagram illustrating an example of an STA grouping methodaccording to an embodiment of the present invention.

FIG. 10 is a diagram illustrating another example of an STA groupingmethod according to the embodiment of the present invention.

FIG. 11 is a diagram illustrating another example of STA groupingaccording to the embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of an STA grouping-basedchannel access method according to an embodiment of the presentinvention.

FIG. 13 is a block diagram illustrating an example of a group assignmentinformation element format according to an embodiment of the presentinvention.

FIG. 14 is a block diagram illustrating another example of a groupassignment information element format according to an embodiment of thepresent invention.

FIG. 15 is a diagram illustrating an example of a channel access methodaccording to an embodiment of the present invention.

FIG. 16 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

FIG. 17 is a block diagram illustrating an example of a channel accessinformation element format.

FIG. 18 is a diagram illustrating an example of a channel access methodaccording to an embodiment of the present invention.

FIG. 19 is a block diagram illustrating another example of a channelaccess information element format according to an embodiment of thepresent invention.

FIG. 20 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

FIG. 21 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

FIG. 22 is a block diagram illustrating an example of a groupingparameter information element format according to an embodiment of thepresent invention.

FIG. 23 is a block diagram illustrating an example of a subgroupingparameter information element format according to an embodiment of thepresent invention.

FIG. 24 is a block diagram illustrating a wireless apparatus toimplement the embodiments of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a view illustrating the configuration of a general WirelessLocal Area Network (WLAN) system to which an embodiment of the presentinvention may apply.

Referring to FIG. 1, the WLAN system includes one or more basic servicesets (BSSs). A BSS is a set of stations (STAs) that may be successfullysynchronized with each other and may communicate with each other, and isnot a concept indicating a specific area.

An infrastructure BSS includes one or more non-Access Point (AP)stations (non-AP STA1(21), non-AP STA2(22), non-AP STA3(23), non-APSTA4(24), and non-AP STAa (30)), an AP 10 providing a distributionservice, and a distribution system (DS) linking multiple APs. In theinfrastructure BSS, the AP manages the non-AP STAs of the BSS.

In contrast, an independent BSS (IBSS) is a BSS operating in an ad-hocmode. The IBSS does not include an AP and thus lacks a centralizedmanagement entity. That is, in the IBSS, non-AP STAs are managed in adistributed manner. In the IBSS, all the STAs may be mobile STAs, anddue to no permission to access the DS, constitute a self-containednetwork.

The STA is any functional entity that includes a medium access control(MAC) and a physical layer interface for a radio medium that follow theInstitute of Electrical and Electronics Engineers (IEEE) 802.11standards and in broader concept includes an AP and a non-AP station.

A non-AP STA is a STA that is not an AP, and may also be referred to asa mobile terminal, wireless device, wireless transmit/receive unit(WTRU), user equipment (UE), mobile station (MS), mobile subscriber unitor simply user. Hereinafter, for ease of description, the non-AP STA isdenoted STA.

The AP is a functional entity that provides access to a DS via a radiomedium for a STA associated with an AP. In an infrastructure BSSincluding an AP, communication between STAs is in principle achieved viaan AP, but in case a direct link is set up, the STAs may perform directcommunication between each other. The AP may also be referred to as acentral controller, base station (BS), node-B, BTS (Base TransceiverSystem), site controller, or managing STA.

A plurality of BSSs including the BSS shown in FIG. 1 may be connectedto each other via a distribution system (DS). The plurality of BSSslinked with each other through a DS is referred to as an extendedservice set (ESS). The APs and/or STAs included in the ESS maycommunicate with each other, and in the same ESS, STAs may travel fromone BSS to another BSS while maintaining seamless communication.

In the WLAN system according to IEEE 802.11, the basic access mechanismof Medium Access Control (MAC) is a Carrier Sense Multiple Access withCollision Avoidance (CSMA/CS) mechanism. The CSMA/CS mechanism is alsoreferred to as Distributed Coordination Function (DCF) of IEEE 802.11MAC, and basically, it adopts a “listen before talk” access mechanism.Following such type of access mechanism, an AP and/or STA senses a radiochannel or medium prior to transmission. If as a result of the sensing,the medium is determined to be in idle state, frame transmission isinitiated through the medium. On the contrary, if the medium is sensedto be in occupied state, the AP and/or STA sets a deferred time formedium access and waits without starting its own transmission.

The CSMA/CS mechanism includes virtual carrier sensing in addition tophysical carrier sensing in which an AP and/or STA directly senses amedium. The virtual carrier sensing is to make up for a problem that mayoccur in connection with medium access, such as hidden node problem. Inorder for virtual carrier sensing, the MAC of the WLAN system makes useof a network allocation vector (NAV). The NAV is a value by which an APand/or STA currently using a medium or having authority to use themedium informs other AP and/or STA of a time remaining until the mediumturns available. Accordingly, the value set by the NAV corresponds to aperiod during which the use of the medium is scheduled by the AP and/orSTA transmitting a frame.

The IEEE 802.11 MAC protocol, together with a DCF, offers a HybridCoordination Function (HCF) that is based on a Point CoordinationFunction (PCF) that periodically performs polling so that all receivingAPs and/or STAs may receive data packets in polling-based synchronizedaccess scheme with the DCF. The HCF has an Enhanced Distributed ChannelAccess (EDCA) that has a contention-based access scheme for providingdata packets to multiple users and HCCA (HCF Controlled Channel Access)that uses contention free-based channel access scheme using a pollingmechanism. The HCF includes a medium access mechanism for enhancingQuality of Service (QoS) of WLAN and may transmit QoS data in both acontention period (CP) and contention free period (CFP).

In the wireless communication system, a STA cannot be immediately awareof the existence of a network due to the characteristics of the radiomedium when a STA powers on and starts operating. Accordingly, in orderto access a network, a STA, whatever type it is, should go through anetwork discovery process. When discovering a network through thenetwork discovery process, the STA selects a network to subscribe tothrough a network selection process. Thereafter, the STA subscribes tothe selected network and performs data exchange at a transmissionend/reception end.

In the WLAN system, the network discovery process is implemented as ascanning procedure. The scanning procedure is separated into passivescanning and active scanning. The passive scanning is achieved based ona beacon frame that is periodically broadcast by an AP. In general, anAP in the WLAN system broadcasts a beacon frame at a specific interval(for example, 100 msec). The beacon frame includes information on a BSSmanaged by it. The STA passively awaits reception of the beacon frame ata specific channel. When obtaining the information on the network byreceiving the beacon frame, the STA terminates the scanning procedure atthe specific channel. The STA need not transmit a separate frame inachieving passive scanning, and the passive scanning is rather done oncethe beacon frame is received. Accordingly, the passive scanning mayreduce the overall overhead. However, it suffers from a scanning timethat is increased in proportion to the transmission period of the beaconframe.

The active scanning is that the STA actively broadcasts a probe requestframe at a specific channel to request that all the APs to receive theprobe request frame send network information to the STA. When receivingthe probe request frame, an AP waits for a random time so as to preventframe collision, and then includes network information in a proberesponse frame, then transmits the probe response frame to the STA. TheSTA receives the probe response frame to thereby obtain the networkinformation, and the scanning procedure is then ended. The activescanning may get scanning done relatively quickly, but may increase theoverall network overhead due to the need of a frame sequence that comesfrom request-response.

When finishing the scanning procedure, the STA selects a network per aspecific standard on itself and then performs an authenticationprocedure alongside the AP. The authentication procedure is achieved in2-way handshake. When completing the authentication procedure, the STAproceeds with an association procedure together with the AP.

The association procedure is performed in two-way handshake. First, theSTA sends an association request frame to the AP. The associationrequest frame includes information on the STA's capabilities. Based onthe information, the AP determines whether to allow association with theSTA. When determining whether to allow association, the AP transmits anassociation response frame to the STA. The association response frameincludes information indicating whether to allow association andinformation indicating the reason for association being allowed orfailing. The association response frame further includes information oncapabilities supportable by the AP. In case association is successfullydone, normal frame exchange is done between the AP and STA. In caseassociation fails, the association procedure is retried based on theinformation on the reason for the failure included in the associationresponse frame or the STA may send a request for association to otherAP.

In order to overcome limit to speed that is considered to be a weaknessin WLAN, IEEE 802.11n has been established relatively in recent years.IEEE 802.11n aims to increase network speed and reliability whileexpanding wireless network coverage. More specifically, IEEE 802.11nsupports high throughput (HT) that reaches data processing speed up to540 Mbps and is based on MIMO (Multiple Inputs and Multiple Outputs)technology that adopts multiple antennas at both transmission end andreception end in order to optimize data speed and minimize transmissionerrors.

As WLAN spreads and more diversified applications using WLAN show up, aneed for a new WLAN system arises for supporting a higher throughputthan the data processing speed supported by IEEE 802.11n. The WLANsystem supporting very high throughput (VHT) is a subsequent version ofthe IEEE 802.11n WLAN system, which is a new one recently suggested tosupport a throughput more than 500 Mbps for a single user and dataprocessing speed more than 1 Gpbs for multiple users in an MAC serviceaccess point (SAP).

Advancing further than the existing WLAN system supporting 20 MHz or 40MHz, the VHT WLAN system intends to support 80 MHz, contiguous 160 MHz,non-contiguous 160 MHz band transmission and/or more bandwidthtransmission. Further, the VHT WLAN system supports 250 QuadratureAmplitude Modulation (QAM) that is more than a maximum of 64QAM of theexisting WLAN system.

Since the VHT WLAN system supports a Multi User-Multiple Input MultipleOutput (MU-MIMO) transmission method for higher throughput, the AP maytransmit a data frame simultaneously to at least one or more MIMO-pairedSTAs. The number of paired STAs may be maximally 4, and when the maximumnumber of spatial streams is eight, each STA may be assigned up to fourspatial streams.

Referring back to FIG. 1, in the WLAN system shown in the figure, the AP10 may simultaneously transmit data to a STA group including at leastone or more STAs among a plurality of STAs 21, 22, 23, 24, and 30associated with the AP 10. In FIG. 1, by way of example, the AP conductsMU-MIMO transmission to the STAs. However, in a WLAN system supportingTunneled Direct Link Setup (TDLS) or Direct Link Setup (DLS) or meshnetwork, a STA to transmit data may send a Physical Layer ConvergenceProcedure (PLCP) Protocol Data Unit (PPDU) to a plurality of STAs usingan MU-MIMO transmission scheme. Hereinafter, an example where an APtransmits a PPDU to a plurality of STAs according to an MU-MIMOtransmission scheme is described.

Data may be transmitted through different spatial streams to each STA.The data packet transmitted by the AP 10 may be referred to as a PPDU,which is generated at the physical layer of the WLAN system andtransmitted, or a frame as a data field included in the PPDU. That is,the PPDU for Single User-Multiple Input Multiple Output (SU-MIMO) and/orMU-MIMO or data field included in the PPDU may be called a MIMO packet.Among them, the PPDU for MUs may be called an MU packet. In the exampleof the present invention, assume that a transmission target STA groupMU-MIMO-paired with the AP 10 includes STA1 21, STA2 22, STA3 23, andSTA4 24. At this time, no spatial stream is assigned to a specific STAin the transmission target STA group, so that no data may be transmittedto the specific STA. Meanwhile, assume that STAa 30 is associated withthe AP but is not included in the transmission target STA group.

In the WLAN system, an identifier may be assigned to the transmissiontarget STA group in order to support MU-MIMO transmission, and thisidentifier is denoted group ID. The AP sends a group ID management frameincluding group definition information for allocating group IDs to theSTAs supporting MU-MIMO transmission and accordingly the group IDs areassigned to the STAs before PPDU transmission. One STA may be assigned aplurality of group IDs.

Table 1 below represents information elements included in the group IDmanagement frame.

TABLE 1 Order Information 1 Category 2 VHT action 3 Membership status 4Spatial stream position

The category field and VHT action field are configured so that the framecorresponds to a management frame and to be able to identify being agroup ID management frame used in a next-generation WLAN systemsupporting MU-MIMO.

As in Table 1, the group definition information includes membershipstatus information indicating whether to belong to a specific group ID,and in case of belonging to the group ID, information indicating thenumber of position to which the spatial stream set of the STAcorresponds in all the spatial streams according to MU-MIMOtransmission.

Since one AP manages a plurality of group IDs, the membership statusinformation provided to one STA needs to indicate whether the STAbelongs to each of the group IDs managed by the AP. Accordingly, themembership status information may be provided in the form of an array ofsubfields indicating whether it belongs to each group ID. The spatialstream position information indicates the position of each group ID, andthus, may be provided in the form of an array of subfields indicatingthe position of a spatial stream set occupied by the STA with respect toeach group ID. Further, the membership status information and spatialstream position information for one group ID may be implemented in onesubfield.

The AP, in case of sending a PPDU to a plurality of STAs through anMU-MIMO transmission scheme, transmits the PPDU, with informationindicating a group identifier (group ID) in the PPDU as controlinformation. When receiving the PPDU, a STA verifies whether it is amember STA of the transmission target STA group by checking the group IDfield. If the STA is a member of the transmission target STA group, theSTA may identify what number of position where the spatial stream settransmitted to the STA is located in the entire spatial stream. The PPDUincludes information on the number of spatial streams allocated to thereceiving STA, and thus, the STA may receive data by discovering thespatial streams assigned thereto.

Meanwhile, TV WS (White Space) draws attention as a newly availablefrequency band in the WLAN system. TV WS refers to an unused frequencyband that is left as the analog TV broadcast is digitalized in the U.S.For example, TV WS includes a 54 to 598 MHz band. However, this ismerely an example, and TV WS may be a permitted band that may be firstused by a licensed user. The licensed user means a user that ispermitted for use of a permitted band, and may also be referred to as alicensed device, primary user, or incumbent user.

The AP and/or STA operating in the TV WS should offer a protectionfunction as to a licensed user, and this is because a licensed user haspriority as to use of a TV WS band. For instance, in case a licenseduser such as a microphone is already using a specific WS channel that isa frequency band split per protocol to have a certain bandwidth in theTV WS band, the AP and/or STA cannot use the frequency bandcorresponding to the WS channel in order to protect the licensed user.Further, the AP and/or STA should stop use of the frequency band if thelicensed user happens to use the frequency band that is being used fortransmission and/or reception of a current frame.

Accordingly, the AP and/or STA should first grasp whether a specificfrequency band in the TV WS band is available, in other words, whetherthere is a licensed user in the frequency band. Grasping whether thereis a licensed user in the specific frequency band is denoted spectrumsensing. As a spectrum sensing mechanism, an energy detection scheme orsignature detection scheme may be utilized. If the strength of areceived signal is higher than a predetermined value, it is determinedthat it is being used by a licensed user, or if a DTV preamble isdetected, it may be determined to be being used by a licensed user.

Always sensing a channel for frame transmission and reception causes theSTA to continue to consume power. The power consumption in the receptionstate makes little difference as compared with the power consumption inthe transmission state, so that keeping the reception state causes theSTA battery powered to consume relatively more power. Accordingly, whenin the WLAN system a STA conducts channel sensing while continuouslymaintaining the reception waiting state, inefficient power consumptionmay arise without particularly increasing WLAN throughput, and thus, itis inappropriate in view of power management.

To compensate for such problems, the WLAN system supports a powermanagement (PM) mode for a STA. The STA power management mode isseparated into an active mode and a power save (PS) mode. The STAoperates basically in the active mode. The STA operating in the activemode maintains an awake state. That is, the STA remains at a state ofbeing able to perform normal operation such as frame transmission andreception or channel sensing.

When in normal operation, the STA shifts between the doze state andawake state. In the doze state, the STA operating with the minimum powerand does not receive radio signals including data frames from the AP.Further, in the doze state, the STA does not conduct channel sensing.

As the STA operates as long as possible, power consumption decreases, sothat the operation period of the STA is increased. However, since frametransmission and reception is impossible in the doze state, it cannot beleft at the operation state unconditionally. In case there is a frame tobe transmitted from the STA operating in the doze to the AP, the STAshifts to the awake state, thereby able to receive frames. However, incase the AP has a frame to be transmitted to the STA operating in thedoze state, the STA cannot receive the frame nor is the STA able to beaware of the existence of the STA. Accordingly, the STA may require theoperations of being aware of whether there is a frame to be sent to theSTA, and if any, shifting to the awake state at a specific period so asto receive the frame. This is described below in connection with FIG. 2.

FIG. 2 is a view illustrating an example of power management operation.

Referring to FIG. 2, the AP 210 sends a beacon frame to STAs in a BSS ata constant period (S210). The beacon frame includes a Traffic IndicationMap (TIM) information element. The TIM element includes informationindicating that the AP 210 buffers a bufferable frame (or bufferableunit BU) for the STAs associated with the AP 210 and that the frame isto be sent. The TIM element includes a TIM used to indicate a unicastframe and a Delivery Traffic Indication Map (DTIM) used to indicate amulticast or broadcast frame.

The AP 210 transmits a DTIM once every three beacon frames oftransmission.

STA1 221 and STA2 222 are STAs operating in PS mode. STA1 221 and STA2222 shift from the doze state to the awake state at every wakeupinterval of a specific period so that the STAs may receive the TIMelement transmitted from the AP 210.

A specific wakeup interval may be configured so that STA1 221 may shiftto the awake state at every beacon interval to thus receive a TIMelement. Accordingly, when the AP 210 first sends out a beacon frame(S211), STA1 221 switches to the awake state (S221). STA1 221 receivesthe beacon frame and obtains the TIM element. In case the obtained TIMelement indicates that a bufferable frame to be sent to STA1 221 isbeing buffered, STA1 221 transmits a PS-poll frame to the AP 210 torequest that the AP 210 send a frame (S221 a). In response to thePS-poll frame, the AP 210 sends a frame to STA1 221 (S231). Whencompletely receiving the frame, STA1 221 turns back to the doze state.

When the AP 210 sends out a second beacon frame, since the medium isoccupied, for example, as if another device gains access to the medium,the AP 210 fails to send a beacon frame at exact beacon interval and maydeferred transmission of the beacon frame (S212). In such case, STA1 221turns its operation mode to the awake state according to the beaconinterval, but cannot receive the deferred beacon frame, so that STA1 221switches back to the doze state (S222).

When the AP 210 sends out a third beacon frame, the beacon frame mayinclude a TIM element that is set as DTIM. However, since the medium isoccupied, the AP 210's transmission of the beacon frame is deferred(S213). STA1 221 switches to the awake state in accordance with thebeacon interval and may obtain the DTIM through the beacon frametransmitted by the AP 210. The DTIM obtained by STA1 221 indicates thatthere is no frame to be transmitted to STA1 221 and that there is aframe for other STA. Accordingly, STA1 221 shifts back to the dozestate. The AP 210, after transmission of the beacon frame, sends a frameto the STA (S232).

The AP 210 sends a fourth beacon frame (S214). However, STA1 221 couldnot obtain the information indicating that a bufferable frame for itselfremains buffered through the previous twice reception of the TIMelement, and thus, STA1 221 may adjust the wakeup interval for receptionof a TIM element. Or, in case the beacon frame transmitted by the AP 210includes signaling information for adjusting the wakeup interval valueof STA1 221, the wakeup interval value of STA1 221 may be adjusted. Inthis example, STA1 221 may change its configuration so that shift of theoperation state for receiving a TIM element is performed at every threebeacon intervals rather than at every beacon interval. Accordingly, STA1221 stays at the doze state after the AP 210 sends a fourth beacon frame(S214) and when the AP 210 transmits a fifth beacon frame (S215), andthus, it cannot obtain the TIM element.

When the AP 210 sends out a sixth beacon frame (S216), STA1 221 switchesto the awake state and obtains the TIM element included in the beaconframe (S224). The TIM element is a DTIM indicating that there is abroadcast frame, so that STA1 221 does not transmit a PS-poll frame tothe AP 210 and receives a broadcast frame transmitted by the AP 210(S234).

Meanwhile, the wakeup interval configured in STA2 222 may have a longerperiod than that of STA1 221. Accordingly, when the AP 210 sends a fifthbeacon frame (S215), STA2 222 may switch to the awake state to receive aTIM element (S225). STA2 222 is aware that there is a frame to be sentthereto through the TIM element, and in order to request transmission,sends a PS-poll frame to the AP 210 (S225 a). The AP 210 sends a frameto STA2 222 in response to the PS-poll frame (S233).

In order to operate the power save mode as shown in FIG. 2, the TIMelement includes a TIM indicating whether there is a frame to be sent tothe STA or a DTIM indicating whether there is a broadcast/multicastframe. The DTIM may be embodied by configuring a field of the TIMelement.

FIG. 3 is a block diagram illustrating an example of a TIM elementformat.

Referring to FIG. 3, the TIM element 300 includes an element ID field310, a length field 320, a DTIM count field 330, a DTIM period field340, a bitmap control field 350, and a partial virtual bitmap field 360.

The element ID field 310 indicates that an information element is a TIMelement. The length field 320 indicates the whole length includingitself and subsequent fields. The maximum value may be 255 and may beset in octets.

The DTIM count field 330 indicates whether a current TIM element is aDTIM, and unless it is a DTIM, indicates the number of remaining TIMsuntil the DTIM is transmitted. The DTIM period field 340 indicates aperiod at which the DTIM is transmitted, and the period at which theDTIM is transmitted may be set as a multiple of the count oftransmission of a beacon frame.

The bitmap control field 350 and the partial virtual bitmap field 360indicate whether a bufferable frame is buffered for a specific STA. Thefirst bit in the bitmap control field 350 indicates whether there is amulticast/broadcast frame to be sent. The remaining bits are set toindicate an offset value to interpret the subsequent partial virtualbitmap field 360.

The partial virtual bitmap field 360 is set as a value indicatingwhether there is a bufferable frame to be sent to each STA. This may beset in the bitmap form where a bitmap corresponding to the AID value ofa specific STA is set as 1. According to the AID order, allocation maybe done from 1 to 2007, and as an example, if the fourth bit is set as1, it means that traffic is buffered in the AP which is to be sent tothe STA whose AID is 4.

Meanwhile, in the circumstance where bits set as consecutive 0's come upfrequently in configuring the bit sequence of the partial virtual bitmapfield 360, using the whole bit sequence configuring the bitmap may beinsufficient. For this, the bitmap control field 350 may contain offsetinformation for the partial virtual bitmap field 360.

FIG. 4 is a view illustrating an example of a bitmap control field and apartial virtual bitmap field according to an embodiment of the presentinvention.

Referring to FIG. 4, the bitmap sequence constituting the partialvirtual bitmap field 360 indicates whether the STA having an AIDcorresponding to the bitmap index includes a buffered frame. The bitmapsequence constitutes indication information on AIDs 0 to 2007.

The bitmap sequence may have consecutive 0's from the first bit to thekth bit. Further, consecutive 0's may be set from the other 1th bit tothe last bit. This indicates that the STAs assigned AIDs 0 to k and theSTAs assigned with 1 to 2007 do not have any buffered frame. As such,the sequence of consecutive 0's from 0^(th) to the kth in the early partof the bitmap sequence may be provided offset information and thesequence of 0's in the latter part may be omitted, thereby reducing thesize of the TIM element.

For this, the bitmap control field 350 may include a bitmap offsetsubfield 351 that contains offset information of a sequence ofconsecutive 0's in the bitmap sequence. The bitmap offset subfield 351may be set to indicate k, and the partial virtual bitmap field 360 maybe set to include the k+1th bit to the 1−1th bit of the original bitmapsequence.

A detailed responding procedure of the STA that has received the TIMelement is described with reference to FIGS. 5 to 7.

FIG. 5 is a flowchart illustrating an example of an AP's respondingprocedure in a TIM protocol.

Referring to FIG. 5, the STA 520 shifts its operation state from dozestate to awake state in order to receive a beacon frame including a TIMfrom the AP 510 (S510). The STA 520 may be aware that there is abuffered frame to be sent thereto by interpreting the received TIMelement.

The STA 520 contends with other STAs for medium access to transmit aPS-poll frame (S520) and sends a PS-poll frame to the AP 510 forrequesting transmission of a data frame (S530).

When receiving the PS-poll frame transmitted from the STA 520, the AP510 sends a frame to the STA 520 (S540). The STA 520 receives the dataframe and in response transmits an ACK (acknowledgement) frame to the AP510 (S550). Thereafter, the STA 520 shifts its operating mode back intothe doze state (S560).

The AP may transmit data at a specific time after receiving the PS-pollframe rather than sending a data frame right after receiving the PS-pollframe from the STA as shown in FIG. 5.

FIG. 6 is a flowchart illustrating another example of an AP's respondingprocedure in a TIM protocol.

Referring to FIG. 6, the STA 620 shifts its operation mode from dozestate to awake state in order to receive a beacon frame including a TIMfrom the AP 610 (S610). The STA 620 may be aware that there is abuffered frame to be sent thereto by interpreting the received TIMelement.

The STA 620 contends with other STAs for medium access for transmissionof the PS-poll frame (S620) and sends the PS-poll frame to the AP 610for requesting the transmission of a data frame (S630).

In case, despite receiving the PS-poll frame, the AP 610 fails toprepare for a data frame for a specific time interval, the AP 610,instead of immediately transmitting a data frame, sends an ACK frame tothe STA 620 (S640). This is a feature of a deferred response differentfrom step S540 in which the AP 510 shown in FIG. 5 sends a data frame tothe STA 520 immediately in response to the PS-poll frame.

The AP 610, if a data frame is ready after transmission of the ACKframe, performs contention (S650), and then sends a data frame to theSTA 620 (S660).

The STA 620 sends an ACK frame to the AP 610 in response to reception ofthe data frame (S670) and switches its operation mode to the doze state(S680).

If the AP sends a DTIM to the STA, a TIM protocol procedure that isperformed thereafter may differ.

FIG. 7 is a flowchart illustrating a procedure of a TIM protocol by aDTIM.

Referring to FIG. 7, STAs 720 switch their operation mode from the dozestate to the awake state in order to receive a beacon frame including aTIM element (S710). The STAs 720 may be aware that a multicast/broadcastframe is to be transmitted through the received DTIM.

The AP 710 sends out a multicast/broadcast frame after transmission ofthe beacon frame including the DTIM (S720). The STAs 720 switch theiroperation state back to the doze state after receiving themulticast/broadcast frame transmitted by the AP 710.

In the power save mode operation method based on the TIM protocoldescribed in connection with FIGS. 2 to 7, the STAs may verify whetherthere is a buffered frame to be transmitted due to buffered trafficthrough the STA identification information included in the TIM element.The STA identification information may be information associated with anAssociation Identifier (AID) that is an identifier assigned when the STAis associated with the AP. The STA identification information may beconfigured to directly indicate the AIDs of the STAs having a bufferedframe or may be configured in the bitmap type in which a bit ordercorresponding to the AID value is set as a specific value. The STAs maybe aware that there is a frame buffered thereto if the STAidentification information indicates its AID.

Hereinafter, Tunneled Direct Link Setup (TDLS) is described.

The TDLS is a protocol to determine negotiation and method between STAsby the STAs in order to avoid and reduce network congestion. In order tosupport DLS between STAs supporting Quality of Service (QoS), managementframes such as a DLS Setup request, a DLS setup response, and a DLSteardown may be transferred between STAs without help from the AP. TheTDLS is based on encapsulation and transmission of management framessuch as a DLS Setup request, a DLS setup response, and a DLS teardown toa data frame.

A procedure of establishing TDLS direct link may be performed throughsignaling between two STAs as illustrated in FIG. 8.

FIG. 8 is a diagram illustrating a signaling procedure to establish TDLSdirect link.

Referring to FIG. 8, a frame may be transceived between a TDLSinitiating STA establishing TDLS direct link and a TDLS peer STA being atarget of establishment of the TDLS direct link.

The TDLS direct link may be established where the TDLS initiating STAtransmits a TDLS setup request frame to the TDLS peer STA through theAP, the TDLS peer STA transmits a TDLS setup response frame through theAP as a response to the TDLS setup request, and the TDLS initiating STAtransmits a TDLS setup confirmation frame to the TDLS peer STA throughthe AP in order to confirm that the TDLS setup response frame isreceived.

When the TDLS direct link is established, the TDLS initiating STA andthe TDLS peer STA may directly transceive the frame without through theAP.

In recent years, an M2M is attracting attention as a next generationcommunication technology. A next generation wireless LAN system supportsthe above M2M. Meanwhile, a TIM protocol to transceive a data frame ofan STA operating in a power save mode in a current wireless LAN systemneeds to consider following M2M related characteristics in order tosupport the M2M.

1. A large number of STAs in the next generation wireless LAN systemsupporting the M2M, the number of STAs associated with one AP may besignificantly more than that of an existing wireless LAN system. Thatis, in the existing wireless LAN system, more STAs than 2007 being themaximum number of AIDs which can be assigned to the STA may beassociated with the AP. In this case, if a reserved AID is used, the AIDmay be assigned to maximum 16383 STAs. A use case of the next generationwireless LAN system for supporting the M2M considers a case where atleast 6000 STAs are associated with the AP.

2. Low transmission rate there are a plurality of applications tosupport a low transmission rate in a wireless LAN system for supportingthe M2M. Accordingly, when the size of bitmap type information includedin the TIM element is large but the TIM element is transmitted with alow rate, a time taken to determine whether a buffered frame for an STAexists is increased as compared with that of the existing LAN system. Inthis case, the STA operating in the power save mode may unnecessarilyconsume power. Accordingly, there is a demand for a scheme capable ofreducing an amount of bitmap type information of the TIM element.

3. Traffic with a very long interval most of STAs for supporting the M2Mhas a traffic which periodically exchanges a small amount of data. Sincea transmission period of the traffic is very long, the number of STAswith a frame capable of receiving from the AP during one beacon periodis less than that of an existing LAN system.

When taking into consideration the foregoing related characteristics ofthe next generation wireless LAN system, if the sizes of the bitmap typeinformation is large but most of the sizes thereof is 0, a method ofcompressing a format of the bitmap type information may be suggested.However, according to a current standard of the wireless LAN system,when the number of STAs exceeds 2008, an existing TIM element is notapplicable as it is. This is because the size of the bitmap typeinformation is considerably increased so that an existing frame formatcannot support the bitmap type information.

A method of implementing information as illustrated in FIG. 4 isapplicable to the method of compressing the bitmap type information.Accordingly, a sequence configuring real bitmap information may beimplemented by a remaining bitmap sequence among entire bitmap sequencesby omitting a sequence composed of continuous 0 at a part before theentire bitmap sequences indicating whether a buffered frame is includedin each STA to provide offset information. In this case, when the numberof STAs with the buffered frame is small but a difference of AIDsassigned to respective STAs is great, it may be inefficient. Forexample, if frames with respect to two STAs to which AIDs with values of10 and 2000 are assigned are buffered, a length of the bitmap typeinformation is 1990 but a value of the bitmap information except forboth ends thereof is 0. That is, when the number of STAs associated withthe AP is small, a great problem may not occur. However, when the numberof STAs is increased so that a value of the assigned AID is increased,it may be difficult to significantly reduce the information bycompressing the bitmap type information in this manner.

In a current WLAN system, the number of stations associated with the APis several tens. However, when the M2M is supported, the number ofassociation stations is rapidly increased. As described above, there isa need for an efficient operating method associated with an AID capableof being set to a very high value in a wireless LAN system in which thenumber of STA associated with the AP may be rapidly increased.

Hereinafter, a method of assigning AID to a large number of (forexample, at least 2007) STAs so that the STAs efficiently approach achannel to transceive data is suggested. To this end, a method ofgrouping STAs is suggested.

The STA grouping according to the present invention may be performedbased on grouping AIDs of an STA. Identification (ID) informationcapable of identifying groups may be applied to each group. Hereinafter,information to identify groups is referred to as ‘group ID’. A followingprovided group ID is ID information different from the above group IDfor MU-MIMO.

There are various methods of grouping the STAs based on AIDs. As oneexample, specific number of bits before an AID assigned to the STA isused as the group ID. This may be implemented as illustrated in FIG. 9.

FIG. 9 is a diagram illustrating an example of an STA grouping methodaccording to an embodiment of the present invention.

Referring to FIG. 9, first two bits B1 and B2 of an AID assigned to anSTA may be set to indicate a group ID of the STA. In the embodiment, thegroup ID is implemented with two bits, total 4 group IDs may beimplemented. All STAs associated with the AP may be grouped as total 4groups. Meanwhile, the number of divided groups may differently set byadjusting the number of bits to indicate the group ID.

As another example of a method of grouping an STA based on an AID, aspecific range of a plurality of AIDs is assigned to a specific STAgroup. For example, when a group ID 1 is expressed as offset A, lengthB, STAs to which AIDs of A to A+B−1 are includes in an STA groupidentified by a group ID 1. An example of the STA grouping may beimplemented as illustrated in FIG. 10.

FIG. 10 is a diagram illustrating another example of an STA groupingmethod according to the embodiment of the present invention.

Referring to FIG. 10, it is assumed that entire AIDs are 1 to N4 AIDs,and an STA is grouped as total 4 STA groups.

AIDs belonging to a group ID 1 are 1 to N1 AIDs, which means that STAsto which AIDs 1 to N1 are assigned are grouped as an STA group accordingto a group ID 1. Meanwhile, corresponding AIDs may be expressed asoffset 1, length N1.

AIDs belonging to a group ID 2 are N1+1 to N2, which means that STAs towhich N1+1 to N2 AIDs are assigned are groups as an STA group accordingto a group ID 2. Meanwhile, corresponding AIDs may be expressed asoffset N1+1, and length N2−N1.

AIDs belonging to a group ID 3 are N2+1 to N3 AIDs, which mean that STAsto which N2+1 to N3 AIDs are grouped as an STA group according to agroup ID 3. Meanwhile, corresponding AIDs may be expressed as offsetN2+1, length N3−N2.

AIDs belonging to a group ID 4 are N2+1 to N3 AIDs, which mean that STAsto which N2+1 to N3 AIDs are grouped as an STA group according to agroup ID 4. Meanwhile, corresponding AIDs may be expressed as offsetN3+1, length N4−N3. STAs to which the same group ID is assigned may beexpressed by offset and a length of an AID.

Meanwhile, when STAs are grouped as shown in FIG. 10, the same number ofAIDs is assigned to a group of each STA. If the number of groups in theSTA is set to a square of 2, as illustrated in FIG. 9, specific bitsbefore a group ID may be used as a group ID to identify an STA group.

According to FIG. 9 and FIG. 10, grouping of the STA may be achievedthrough one step. However, the grouping of the STA may be achievedthrough a plurality of steps. For example, entire STAs may be grouped asan STA group, and an STA included in a specific STA group may be groupedas an STA subgroup. In this case, the first specific bits of a bitsequence configuring an AID are a group ID to identify an STA group, andspecific bits after the first specific bits of a bit sequence may beused as a subgroup index to identify an STA-sub group. This may beimplemented as illustrated in FIG. 11.

FIG. 11 is a diagram illustrating another example of STA groupingaccording to the embodiment of the present invention.

Referring to subfigure (a) of FIG. 11, first two B1 and B2 in an AID bitsequence may be set to indicate a group ID of an STA, and next threebits B3, B4, and B5 may be set to indicate a subgroup index of an STA.

In an example of STA grouping in subfigure (b) of FIG. 11, since a groupID is implemented with 2 bits, total 4 group IDs may be implemented, andall STAs may be grouped as total 4 groups. Since a subgroup index isimplemented with 3 bits, total 8 subgroup indexes may be implemented,and STAs included in a specific STA group may be grouped as total 8 STAsubgroups.

As shown in FIG. 11, when the STA grouping is performed, a specific STAgroup may be indicated, and a specific subgroup belonging to a specificSTA may be indicated based on a group ID and a subgroup index.

In addition, at least one STA subgroup may be indicated based on a groupID, subgroup off and a subgroup length. The subgroup offset indicates anSTA subgroup having the smallest subgroup index in at least one STAsubgroup among a plurality of STA subgroups of an STA group indicated bya group ID. The subgroup length indicates the number of STAs of acontinuous index including an STA subgroup indicated by the subgroupoffset. For example, when grouping is performed as illustrated in FIG.11( b), STA subgroups 3 to 5 of an STA group 1 may be indicated througha group ID 1(00), subgroup offset 3(010), and a subgroup length 3.

Meanwhile, the number of bits in FIG. 11 is illustrative purpose onlyand a group ID and a subgroup index may be implemented through bitshaving various lengths. A range of the present invention may include anexample of a simple variation of the number of bits.

If the STA is grouped, STAs may access a channel at different timeintervals according a group ID and/or a subgroup index. When the STAsoperate in a power save mode, the STAs enter an awake state at a channelaccess period for the STAs to access the channel. If the channel accessperiod is terminated, the STAs may enter a sleep state. Accordingly, aproblem associated with an over load due to an increased TIM size whichmay be caused by a large number of STAs and a channel access problem maybe solved, and data may be efficiently transceived. Further, anefficiency of the power save mode may be increased. An example of achannel access according to the STA group is illustrated in FIG. 12.

FIG. 12 is a diagram illustrating an example of an STA grouping-basedchannel access method according to an embodiment of the presentinvention.

FIG. 12 illustrates an example of a channel access method of differentlysetting a channel access interval by STA groups.

Referring FIG. 12, when entire STAs are grouped as three STA groups, achannel access mechanism according to a beacon interval is shown.

A first beacon interval is a first channel access period for an STAgroup 1 according to a group ID 1. Accordingly, a beacon frame of thefirst beacon period may include a channel access information elementindicating that STAs included in an STA group indicated by a group ID 1may approach a channel. The STAs may determine whether the STAs mayaccess a channel during a corresponding period through the channelaccess information element. Further, a beacon frame may include a TIMelement for STAs included in a corresponding STA group. The TIM elementmay include bitmap information implemented to indicate whether there isa frame buffered through AIDs associated with a corresponding STA group.Accordingly, STAs included in an STA group 1 may access a channel totransceive data with the AP during a first channel access period.

A second beacon period is a second channel access period for an STAgroup 2 according to a group ID 2. Accordingly, a beacon frame of thesecond beacon period may include a channel access information elementindicating that STAs included in an STA group indicated by a group ID 2may approach the channel. The STAs may determine whether the STAs mayaccess a channel during a corresponding period through the channelaccess information element. Further, a beacon frame may include a TIMelement for STAs included in a corresponding STA group. The TIM elementmay include bitmap information implemented to indicate whether there isa frame buffered through AIDs associated with a corresponding STA group.Accordingly, STAs included in an STA group 2 may access a channel totransceive the data with the AP during a second channel access period.

A third beacon period is a third channel access period for an STA group3 according to a group ID 3. Operation of STAs in a corresponding periodmay be performed as described above.

A fourth beacon interval is a second channel access period for an STAgroup 1 according to a group ID 1. A fifth beacon interval is a secondchannel access period for an STA group 2 according to a group ID 2. Asixth beacon interval is a third channel access period for an STA group3 according to a group ID 2. That is, when entire STAs are grouped asthree STA groups, channel access periods for three STA groups may beperiodically repeated and formed.

In the channel access method as illustrated in FIG. 12, STAs of adifferent STA group may approach the channel every channel accessperiod. Accordingly, the AP may generate bitmap information capable ofindicating whether there is a buffered frame with respect to an STAgroup capable of accessing at a corresponding channel access period inorder to generate a TIM element. Referring to FIGS. 9 to 11, since aspecific STA group is a set of STAs to which an AID in a specific AIDrange is assigned, the size of bitmap information is reduced togetherwith offset information and the bit information may configure efficientinformation capable of indicating presence of a buffered frame. That is,in the STA grouping-based channel access method, when the number of STAsare very large so that the number of assigned AIDs is more than that ofexisting AIDs, since grouping of the STA may be performed based on theAID, an efficient TIM element may be generated. Accordingly, data may beefficiently transceived based on a TIM protocol.

Meanwhile, although STA group of one step is performed in such a waythat one STA group accesses during each beacon interval in an example ofa channel access method shown in FIG. 12, the present invention suggestvarious channel access schemes. A channel access scheme according to theembodiment of the present invention may further assign a channel accessperiod for a STA subgroup according to a grouping step of an STA. Eachchannel access period may be assigned to at least one STA group and/orat least one STA subgroup during one beacon interval. The channel accessmethod according to the present will be described in detail later.

The AP may indicate an AID of an STA through AID fields of anassociation response frame and/or a reassociation response frame inorder to assign an AID of the STA. Meanwhile, if the STA is groupedbased on the AID, the AP may assign the AID to the STA and providegrouping related information. When the STA is grouped through one step,the AP may report the AID and a group ID to the STA. When the STA isgrouped through at least two steps, the AP may provide detailed groupingrelated ID information as well as an AID, a group ID, and a subgroupindex. In order to report grouping related information to the STA, agroup assignment information element may be defined, and the groupassignment information element may be included in an associationresponse frame and/or a reassociation response frame to be transmitted.

FIG. 13 is a block diagram illustrating an example of a group assignmentinformation element format according to an embodiment of the presentinvention.

Referring to FIG. 13, the group assignment information element 1300includes an element ID field 1310, a length field 1320, a groupinformation field 1330, a Current Group ID field 1340, and a Number ofGroup ID field 1350.

The element ID field 1310 may set to indicate that a correspondinginformation element is a group assignment information element 1200.

The length field 1320 may be set to indicate a total length of a bitsequence configuring other fields included in the group assignmentinformation element 1300 after the length field 1320.

The group information field 1330 includes grouping information for anSTA for receiving the group assignment information element. The groupinformation field 1330 may include a group ID sub-field 1331, a CurrentNumber of AID sub-field 1332, and a Total Number of AID sub-field 1333.

The group ID sub-field 1331 may be set to indicate a group ID toidentify an STA group including an STA.

The Current Number of AID sub-field 1332 may indicate the number of AIDsincluded in an STA group according to the group ID indicated by thegroup ID sub-field 1331, and may indicate the number of STAs included inan STA group according to the group ID.

The Total Number of AID sub-field 1333 may indicate the Total number ofAIDs which may be included in an STA group according to the group IDindicated by the group ID sub-field 1331. The Total Number of AIDsub-field 1333 may indicate the total number of STAs which may beincluded in an STA group according to a group ID.

The Current Group ID field 1340 may indicate a group ID of an STA groupin which a channel access is allowed when corresponding information istransferred to the STA.

The Number of Group ID field 1350 may indicate the total number of STAgroups.

In a channel access method of assigning a channel access period for anSTA group according to a specific group ID by beacon intervals, the STAmay determine a channel access period for an STA group to which the STAbelongs through the Current Group ID field 1340 and the Number of GroupID field 1350. Accordingly, the STA may receive a beacon frame accordingto a corresponding channel access period to receive a buffered framefrom an AP when there is a frame buffered through a TIM element, and maytransceive the data with the AP during a corresponding channel accessperiod.

Meanwhile, the AID may be assigned to the STA according to a device typeof the STA. One AID in a specific AID range may be assigned to the STAof a specific device type. When STA group is performed based on the AID,the STA grouping may be performed according to a device type.

For example, two STA groups are set and accordingly AIDs may be dividedinto two groups. An AID belonging to a first STA group may be assignedto an STA to be used for over load. An AID belonging to a second STAgroup may be assigned to an STA to be used for sensor/meter.

Meanwhile, required device characteristics may be changed according to adevice type. As one example of the characteristics, so as to reducepower consumption according to a device type, a maximum transmissionpower limit value may be differently set. Accordingly, a group of theSTA is assigned, information to indicate a maximum transmission powervalue may be provided. This may be performed by FIG. 4 and providing agroup assignment information element.

FIG. 14 is a block diagram illustrating another example of a groupassignment information element format according to an embodiment of thepresent invention.

Referring to FIG. 14, the group assignment information element 1400includes an element ID field 1410, a length field 1420, a groupinformation field 1430, a current group ID field 1440, and a number ofgroup ID field 1450. However, the element ID field 1410, since thelength field 1420, the group information field 1430, the current groupID field 1440, and the number of group ID field 1450 of the groupassignment information element 1400 are the same as the element ID field1310, the length field 1320, the group information field 1330, thecurrent group ID field 1340, and the number of group ID field 1350 ofthe group assignment information element 1330 of FIG. 13, respectively,a detailed description thereof is omitted.

The group information field 1430 of the group assignment informationelement 1400 includes a group ID sub-field 1431, a maximum transmissionpower sub-field 1432, a current number of AID sub-field 1433, and atotal number of AID sub-field 1434. Since the group ID sub-field 1431,the Current Number of AID sub-field 1433, and the Total Number of AIDsub-field 1434 are the same as the group ID sub-field 1331, the CurrentNumber of AID sub-field 1332, and the Total Number of AID sub-field 1333shown in FIG. 13, respectively, a detailed description thereof isomitted.

The maximum transmission power sub-field 1432 may indicate a limitationvalue of maximum transmission power which an STA group according to agroup ID indicated by a group ID sub-field 1431 can use. A specific AIDincluded in a specific AID range may be assigned to an STA of a specificdevice type and may be included in an STA group with limited maximumtransmission power. Further, data transception with the AP may beperformed during a channel access period using transmission power withina limitation value indicated by the maximum transmission power sub-field1432.

Although the channel access method is described with reference to FIG.12, various channel access method based on STA grouping will be nowdescribed.

FIG. 15 is a diagram illustrating an example of a channel access methodaccording to an embodiment of the present invention.

Referring to FIG. 15, one beacon interval may include three channelaccess periods.

Each channel access period may be set for each STA. According to theembodiment, STAs belonging to an STA group 1 during a first beaconinterval access a channel during a first channel access period totransceive the data with the AP. Next, STAs belonging to an STA group 2access a channel during a second channel access period to transceive thedata with the AP, and STAs belonging to an STA group 3 access a channelduring a third channel access period to transceive data with the AP.During a second beacon interval, a channel access period according tothe first beacon interval may be repeated and formed.

In FIG. 15, channel access periods in one beacon interval are equallyassigned by the total number of STA groups, and the channel accessperiods are sequentially assigned in the order of the STA groups.Accordingly, although special information is not included in a beaconframe, an STA knowing the total number of STA groups and an STA group towhich the STA belongs may recognize when starts and terminates a channelaccess period.

Meanwhile, unlike FIG. 15, a channel access period is not equallyassigned to each STA group in one beacon interval, and an assignmentorder of the channel access period may be assigned regardless of theorder of the STA groups. The channel access method may be performed withreference to FIG. 16.

FIG. 16 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

Referring to FIG. 16, it may be understood that a plurality of channelaccess periods are assigned in one beacon interval, and lengths ofrespective access periods are set differently from each other. In thiscase, an STA additionally needs information on a corresponding channelaccess period to access a channel according to a channel access periodfor an STA group to which the STA belongs. To this end, the beacon framemay include a channel access information element.

FIG. 17 is a block diagram illustrating an example of a channel accessinformation element format.

Referring to FIG. 17, the channel access information element 1700includes an element ID field 1710, a length field 1720, a group ID field1731, a channel access period start field 1732, and a channel accessperiod duration field 1733.

The element ID field 1710 may be set to indicate that a correspondinginformation element is a channel access information element 1700.

The length field 1720 may be set to indicate a total length of a bitsequence configuring fields included after the length field 1720 in thechannel access information element 1700.

The group ID field 1731, the channel access period start field 1732, andthe channel access period duration field 1733 implement information on achannel access period with respect to a specific STA group.

The group ID field 1731 may include a group ID associated with an STAgroup capable of accessing a channel during a channel access periodspecified by the channel access period start field 1732 and the channelaccess period duration field 1733.

The channel access period start field 1732 indicates a time point when achannel access period for an STA group indicated by the group ID field1731 starts. A value indicated by the channel access period start field1732 may indicate a time interval to a start time point based on abeacon frame transmission time point when the channel access informationelement 1700 is included and transmitted.

The channel access period duration field 1733 may be set to indicate aduration time of a channel access period for an STA group indicted bythe group ID field 1731.

Meanwhile, The group ID field 1731, the channel access period startfield 1732, and the channel access period duration field 1733 may berepeatedly included by the number of channel access periods assigned ina beacon interval associated with a beacon frame to which the channelaccess information element 1700 is included and transmitted.Accordingly, when the STA interprets the channel access informationelement 1700 of the beacon frame, the STA may know how many fields of achannel access period are repeated in a corresponding informationelement through a value of the length field 1720.

Referring back to FIG. 16, a first beacon interval and a second beaconinterval include three channel access periods, respectively.Accordingly, a channel access period information element withinformation on a channel access period in the first beacon interval anda channel access period information element with information on achannel access period in the second beacon interval may include fieldsfor a first channel access period, fields for a second channel accessperiod, and fields for a third channel access period.

STAs may determine a period when the STAs may approach a channel basedon a channel access period information element of a beacon frame. EachSTA may access the channel at a channel access period for each STA toexchange data with the AP. When a current period is a channel accessperiod for an STA operating in a power save mode, the STA operates in asleep state. If the channel access period for the STA starts, the STAmay enter an awake state to operate.

Meanwhile, in the STA grouping-based channel access method, all STAs mayaccess a channel during a corresponding period by setting a specificperiod being all channel access period and may be set to exchange datawith the AP. Only specific STAs which are not associated with the APduring the specific period being all channel access period may beimplemented to transmit a frame to the AP through a channel access.

When all channel access period is set, the channel access method may beperformed as illustrated in FIG. 18.

FIG. 18 is a diagram illustrating an example of a channel access methodaccording to an embodiment of the present invention.

Referring to subfigure (a) of FIG. 18, a specific beacon interval may beset as all channel access period. The subfigure (a) may illustrate anexample when all channel access period are added in a channel accessmethod as illustrated in FIG. 12.

In a case of the subfigure (a), since a channel access period withrespect to one STA group is set in a beacon interval, the beacon framemay be transmitted to include a TIM for a corresponding STA group. Inthis case, an operation of receiving a buffered frame based on the TIMmay be performed during a channel access period for the STA group.

Referring to subfigure (b) of FIG. 18, all channel access period and achannel access period for a specific STA group may be assigned in thebeacon interval. According to an example shown in the subfigure (b), itmay be understood that duration times of all channel access period and achannel access period for a specific STA group are the same as eachother, and all channel access period are set after transmission of thebeacon frame. In this case, the STA may not clearly receive informationon a channel access period set in a corresponding beacon interval butmay distinguish the all channel access period from the channel accessperiod for the specific STA group. This is because the STA know thatchannel access periods are sequentially set by STA groups and a channelaccess period for a specific STA group starts after half of the beaconinterval. Accordingly, the STA may determine whether the STA has achannel access authority during a channel access period for a specificSTA group to operate.

In a case of the subfigure (b), the all channel access period isdisclosed before the channel access period for the specific STA group,which is illustrative purpose only. That is, a method where the allchannel access period is disclosed after the channel access period forthe specific STA group may be considered.

Referring to subfigure (c) of FIG. 18, the all channel access period andchannel access periods for respective STA groups may be set in thebeacon interval to have an equal duration time. Since the STA may knowthat the all channel access period and channel access periods forrespective STA groups are sequentially set in the beacon interval, theSTA may access the channel during a channel access period for an STAgroup to which the STA belongs to exchange data with the AP. Meanwhile,the all channel access period may be implemented according to setting sothat all STAs may access the channel or an STA which is not associatedwith the AP may access the channel.

As shown, the all channel period is disclosed before channel accessperiods for respective STA groups, which is illustrative purpose only.That is, a method may be considered where the all channel period isdisclosed after channel access periods for STA groups.

Referring to subfigure (d) of FIG. 18, the all channel access period ofan STA group may be set in a beacon interval before channel accessperiods for respective STA groups.

In scheduling of various channel access periods shown in FIG. 18, sinceinformation on at least one channel access period assigned in acorresponding beacon interval is included in a transmission beacon frameto be transmitted from the AP, the information is transferred to the STAso that information on the channel access period may be shared betweenthe AP and the STA. In this case, the information on the channel accessperiod may be the above channel access information element. Signalingwith respect to scheduling of a channel access period is previouslyachieved between the STA and the AP so that information on the channelaccess period may be shared.

According to the channel access method described with reference to thedrawings, there has been suggested a method where channel access periodsare set by STA groups and each STA accesses a channel according to achannel access period to exchange data with the AP. Meanwhile, as shownin FIG. 11, STAs may be grouped as STA subgroups. In this case, thechannel access period is set with respect to an STA group and/or an STAsubgroup, and each STA accesses a channel according to a preset channelaccess period to exchange data with the AP.

FIG. 19 is a block diagram illustrating another example of a channelaccess information element format according to an embodiment of thepresent invention.

Referring to FIG. 19, the channel access period information element 1900includes an element ID field 1910, a length field 1920, a group ID field1930, a subgroup ID field 1940, a channel access period start field1950, and a channel access period duration field 1960.

The element ID field 1910 may be set to indicate that a correspondinginformation element is a channel access information element 1900.

The length field 1920 may be set to indicate a total length of a bitsequence configuring fields included after the length field 1920 in thechannel access information element 1900.

The group ID field 1930 and the subgroup ID field 1940 implement an STAgroup and/or at least one STA subgroup capable of accessing a channelduring a channel access period specified by the channel access periodstart field 1950 and the channel access period duration field 1960.

When the channel access period is a channel access period for a specificSTA group, the group ID field 1930 includes a group ID associated with acorresponding STA group, and the subgroup ID field 1940 may be set toindicate a value (e.g. Null value) which is not specified. In this case,the channel access period start field 1950 and the channel access periodduration field 1960 specify a channel access period for a correspondingSTA group.

When the channel access period is a channel access period for at leastone STA subgroup, the group ID field 1930 may be set to include a groupID associated with an STA group with at least one STA subgroup.Meanwhile, the subgroup ID field 1940 may be implemented in two schemes.

Referring to subfigure (a) of FIG. 19, a subgroup ID field includes asubgroup index sub-field 1940 a. The subgroup index sub-field 1940 a mayindicate a subgroup index associated with an STA subgroup capable ofaccessing the channel during a channel access period specified by thechannel access period start field 1950 and the channel access periodduration field 1960.

Referring to subfigure (b) of FIG. 19, a subgroup ID field 1940 bincludes a group offset sub-field 1941 b and a subgroup length field1942 b. The group offset sub-field 1941 b indicates an STA subgrouphaving the smallest subgroup index in at least one STA subgroup among aplurality of STA subgroups of an STA group indicated by the group IDfield 1930. The group offset sub-field 1942 b indicates the number ofSTA subgroups of continuous indexes including an STA subgroup indicatedby the group offset sub-field 1941 b. Accordingly, at least one STAsubgroup may be indicated by the group ID field 1930, the group offsetsub-field 1941 b, and a subgroup length field 1942 b.

The channel access period start field 1950 indicates a time point when achannel access period for at least one STA subgroup indicated by thegroup ID 1930 and the subgroup ID field 1940 starts. The channel accessperiod duration field 1960 may be set to indicate a duration time of achannel access period for at least one STA subgroup indicated by thegroup ID 1930 and the subgroup ID field 1940.

FIG. 20 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

Referring to FIG. 20, an STA1 is included in an STA subgroup indicatedby a group ID 2 and a subgroup index 4. An STA2 is included in an STAsubgroup indicated by a group ID 1 and a subgroup index 3. An STA3 isincluded in an STA subgroup indicated by a group ID 1 and a subgroupindex 1.

The STA1, the STA2, and the STA3 enters an awake state at a transmissiontime point of a beacon frame to receive the beacon frame and a channelaccess information element of a format as illustrated in FIG. 19 isincluded in the beacon frame so that the beacon frame is transmitted.The STA1 to STA3 acquire information on a channel access period througha channel access information element.

The STA1 to STA3 may determine whether a channel access period thereforstarts through a group ID field and a subgroup ID field of the channelaccess information element.

Since the group ID field indicates a group ID 1, the STA 1 confirms thatthe information is not information on a channel access period for theSTA1. Accordingly, the STA1 may maintain a sleep state to operate afterreception of the beacon frame.

Since a group ID field indicates a group ID 1 and a subgroup ID fieldindicates a subgroup index 3, an STA2 may determine whether informationon the channel access period is information for the STA2. Accordingly,the STA2 enters an awake state at a time point indicated by a channelaccess period start field to exchange data with the AP during a durationtime indicated by the channel access period duration field. If thechannel access period is terminated, the STA2 again enters a sleepstate.

Since a group ID field indicates a group ID 1 but a subgroup ID fieldindicates a subgroup index 1, an STA3 confirms that the information isnot information on a channel access period for the STA3. Accordingly,the STA3 may maintain a sleep state to operate after reception of thebeacon frame.

FIG. 21 is a diagram illustrating another example of a channel accessmethod according to an embodiment of the present invention.

Referring to FIG. 21, STAs 1 include at least one STA included in STAsubgroups indicated by a group ID 2, a subgroup index 2, and a subgroupindex 3. STAs 2 includes at least one STA included in STA subgroupsindicated by a subgroup index 5 and a subgroup index 6. STAs 3 includesat least one STA included in STA subgroups indicated by a group ID 3, asubgroup index 1, and a subgroup index 2.

The STAs 1, the STAs 2, and the STAs 3 enter an awake state at atransmission time point of a beacon frame to receive the beacon frame,and a channel access information element of a format as illustrated inFIG. 19 is included in the beacon frame so that the beacon frame istransmitted. The STAs 1 to STAs 3 acquire information on the channelaccess period through the channel access information element.

The STAs 1 to STAs 3 may determine whether the channel access periodtherefor starts through a group ID field and a subgroup ID field of thechannel access information element. The group ID field of the channelaccess information element indicates the group ID 3, and the subgroupoffset sub-field indicates a subgroup index 4 and a subgroup lengthsub-field. Accordingly, it is understood that a corresponding channelaccess period is for STA subgroups indicated by subgroup indexes 4, 5,and 6 of an STA group indicated a group ID 3.

Since the group ID field indicates the group ID 3, the STAs 1 confirmsthat the information is information on a channel access period therefor.Accordingly, the STAs 1 may maintain a sleep state to operate afterreception of the beacon frame.

Since the group ID field indicates a group ID 3, and a subgroup offsetof the subgroup ID field and a subgroup length sub-field indicates STAsubgroups according to subgroup indexes 4, 5, and 6, the STAs 2 maydetermine that information on the channel access period is informationtherefor. Accordingly, the STAs 2 enter an awake state at a time pointindicated by a channel access period start field to exchange data withthe AP during a duration time indicated by a channel access periodduration field. If the channel access period is terminated, the STAs 2again enter a sleep state.

Since the group ID field indicates the group ID 3 but subgroup offset ofthe subgroup ID field and the subgroup length sub-field indicate STAsubgroups according to subgroup indexes 4, 5, and 6, STAs 3 confirm thatthe formation is information on the channel access period therefor.Accordingly, the STAs 3 may maintain a sleep state to operate afterreception of the beacon frame.

The above channel access method based on STA grouping may perform STAgrouping based an AID of an STA to divide and assign channel accessperiods by STA groups. Each STA group or each STA subgroup may exchangedata with the AP during a channel access period assigned thereto.Accordingly, a wireless LAN system with very many STAs may efficientlyexchange the data by STA groups.

Meanwhile, an AP may dynamically correct the number of STA groups andthe number of terminals belonging to each STA group. In this manner, aTIM protocol may be more efficiently operated by dynamically adjustingthe number of STA groups and the number of STAs included in each STAgroup. To this end, there is a need to efficiently update a groupingparameter to change STAs. To this end, the AP transfers groupingparameter information to the STAs at a predetermined time interval, andthe STAs hears a corresponding grouping parameter to synchronize thegrouping parameter information with the AP.

When STAs are grouped as STA groups 1, 2, and 3, the STAs receive afirst beacon frame starting grouping in order to hear grouping parameterfrom the AP. In general, since all STAs receive a beacon frame at a DTIMinterval, a first beacon frame starting the grouping, that is, a beaconframe including a grouping parameter may be a beacon frame with a DTIM.The DTIM Beacon frame includes the grouping parameters illustrated inFIG. 13 and FIG. 14. Further, the STAs may indicate whether there is abuffered traffic with respect to terminals belonging to each STA groupto the STAs in the form of a bitmap by group IDs.

FIG. 22 is a block diagram illustrating an example of a groupingparameter information element format according to an embodiment of thepresent invention.

Referring to FIG. 22, a grouping parameter information element 2200includes an element ID field 2210, a length field 2220, a current groupID field 2230, a number of group ID field 2240, a total number of AIDfield per STA group 2250, and a group ID bitmap field 2260.

The element ID field 2210 may be set to indicate that a correspondinginformation element is a grouping parameter information element 2200.

The length field 2220 may be set to indicate a length of the groupingparameter information element 2200 and/or a length of a bit sequenceconfiguring fields included after the length field 2220 in the groupingparameter information element 2200. Meanwhile, the length field 2220 maybe set to indicate a length of the group ID bitmap field 2260. The STAreceiving the grouping parameter information element 2200 may calculatea variable length of the group ID bitmap field 2260 through informationindicated by the length field 2220.

The current group ID field 2230 may indicate a group ID which the APwants to update group ID related information through the groupingparameter information element 2200. When the AP updates a plurality ofgroup IDs, it may be interpreted that a group ID indicated by thecurrent group ID field 2230 indicates a first group ID among a pluralityof updated group IDs. For example, when grouping parameters associatedwith group IDs 1, 2, and 3 are updated, the current group ID field 2230may indicated the group ID 1. Meanwhile, a form expressing the group IDmay refer to FIGS. 9 to 11.

The AP may dynamically correct the number of STA groups and the numberof terminals belonging to each STA group. To this end, the AP may setand add the number of group ID field 2240 and the total number of AIDfield per STA group 2250 into the grouping parameter information element2200 to transmit the grouping parameter information element 2200.

The number of group ID field 2240 may indicate the number of STA groupsin which grouping information is updated through the grouping parameterinformation element 2200. The TIM element may be provided per STA group.

The total number of AID field per STA group 2250 may indicate the totalnumber of AIDs belonging to an STA group, and may be interpreted toindicate the number of STAs belonging to each STA group. The totalNumber of AID per STA group 2250 may indicate an AID range covered withTIM elements of each STA group.

The group ID bitmap field 2260 indicates whether there is a bufferedframe per STA group, and may be implemented as a bitmap sequence.

For example, when the current group ID field 2230 indicates a group ID 1and the number of group ID field 2240 indicates a group ID 3, if thegroup ID bitmap field 2260 indicates 0, 0, 1, it means that there is nobuffered frame with respect to STAs belonging to STA groups 1 and 2according to the group ID 1 and the group ID 2. Meanwhile, it means thatthere is a buffered frame with respect to STAs belonging to the STAgroup 3 according to the group ID 3. Accordingly, the STAs belonging tothe STA group 3 may enter an awake state during a channel access periodfor the STA group 3, and may receive a TIM element from the AP toconfirm whether there is a frame buffered therein.

Bitmap information of the TIM element may be implemented to indicatewhether there are buffered frames for STAs to which a specific STA groupbelongs. That is, although an existing TIM element includes bitmap typeinformation to indicate whether there are buffered frames with respectto entire STAs, a TIM element transmitted during a channel access periodfor the specific STA group may include bitmap type information withrespect to a corresponding STA group in a wireless LAN system to whichthe grouping parameter information element is applied. The TIM elementmay further include a group ID field in order to indicate an STA groupto which the included bitmap type information is applied.

If the STA confirms that there is a buffered frame for an STA group towhich the STA belongs, the STA may receive a TIM element during achannel access period for a corresponding STA group to confirm that acorresponding TIM element includes information for the corresponding STAgroup. When the STA confirms that the TIM element is information for thecorresponding STA group, the STA may determine whether there is abuffered frame for the STA based on bitmap type information. When thereis the buffered frame for the STA, the STA may request transmission ofthe buffered frame to the AP during a channel access period to acquirethe buffered frame.

In this manner, when the TIM element is implemented, an overhead due tothe bitmap type information included in the TIM element may be reducedas compared with that of the related art, and a TIM protocol basedbuffered traffic may be efficiently processed.

If the STA receives the grouping parameter information element 2200through a beacon frame transferring a DTIM and/or a beacon frametransferring a TIM, the STA may be operated during a channel accessperiod for the STA according to a newly grouped STA group. That is, theSTA may enter an awake state during the channel access period toexchange data with the AP, and may enter a doze state to operate duringremaining periods.

The grouping parameter information element associated with update of theabove grouping parameter and an operation of the STA according to thegrouping parameter information element are applicable associated withSTA subgroups.

FIG. 23 is a block diagram illustrating an example of a subgroupingparameter information element format according to an embodiment of thepresent invention.

Referring to FIG. 23, a subgrouping parameter information element 2300may include an element ID field 2310, a length field 2320, a group IDfield 2330, a number of subgroup field 2340, and a subgroup index bitmapfield 2350.

The element ID field 2310 may be set to indicate that a correspondinginformation element is the subgrouping parameter information element2300.

The length field 2320 may be set to indicate a length of the subgroupingparameter information element 2300 and/or a length of a bit sequenceconfiguring fields included after the length field 2320 in thesubgrouping parameter information element 2300. Meanwhile, the lengthfield 2320 may be set to indicate a length of the subgroup index bitmapfield 2350. The STA receiving the grouping parameter information element2300 may calculate a variable length of the subgroup index bitmap field2350 through information indicated by the length field 2320.

The group ID field 2330 may include a group ID to identify a group STAassociated with the grouping parameter information element 2300. Thatis, the AP may indicate a group ID to identify an STA group in order tosubgroup related information through the grouping parameter informationelement 2300.

The number of subgroup field 2340 may indicate the number of STAsubgroups divided from a STA group indicated by the group ID field 2330.

The subgroup index bitmap field 2350 indicates whether there is abuffered frame per the STA subgroup. When the number of subgroup field2340 indicates 4, the subgroup index bitmap field 2350 may indicatewhether there is a buffered frame with 4 STA subgroups as a bitmap type.If the subgroup index bitmap field 2350 indicates 0, 0, 0, 1, it meansthat there is no buffered frame with respect to STAs belonging to STAsubgroups 1 to 3 according to subgroup indexes 1 to 3. Accordingly,since STAs belonging to STA subgroups 1 to 3 of a corresponding STAgroup know that there is no buffered frame therefor although the STAsreceive a TIM element in a channel access period for a corresponding STAsubgroup afterwards, the STAs may not request transmission of thebuffered frame.

In contrast, it means that there is a buffered frame with respect toSTAs belonging to an STA subgroup 4 according to a subgroup index 4.Accordingly, STAs included in the STA subgroup 4 may enter an awakestate during a channel access period for an STA subgroup 4 of acorresponding STA group and may receive a TIM element from the AP toconfirm whether there is a frame buffered therein.

The TIM element includes bitmap type information to identify whetherthere is a buffered frame with respect to STAs included in a specificSTA subgroup of a specific STA group. Accordingly, the TIM element mayinclude information to indicate an STA group and an STA subgroupcorresponding to the included bitmap type information. To this end, theTIM element may further include a group ID field and a subgroup index IDfield. An STA receiving the TIM element may determine whether acorresponding TIM element includes bitmap type information to indicatepresence of a buffered frame for the STA based on a group ID field and asubgroup index field. Further, the bitmap type information may beimplemented by a bitmap sequence mapped to STAs included in at least oneSTA subgroup indicated by the group ID field and the subgroup indexfield. Accordingly, the STA may receive the bitmap type information toconfirm whether there is a buffered frame for the STA. When there is thebuffered frame for the STA, the STA may request transmission of thebuffered frame to the AP.

When STAs receiving the subgrouping parameter information element 2300operate in a power save mode, the STAs may enter an awake state toexchange data with the AP during a channel access period with respect toan STA subgroup to which the STAs belong, and may enter a sleep state tooperate during remaining periods.

The above subgrouping parameter information element may be added to afirst beacon frame to which a DTIM is transmitted and/or a second beaconframe to which a TIM is transmitted so that the first beacon frameand/or the second beacon frame may be transmitted.

The data can be transceived based on the TIM element with compressedbitmap type information through the grouping parameter informationelement and the subgrouping parameter information element. This maysignificantly reduce the overhead according to an existing TIM elementto provide efficient TIM element based data transception. Further, STAscorresponding to a channel access period request transmission of abuffered frame to the AP so that a throughput rate of data can beimproved and remaining STAs operates in a sleep state to increase powersave efficiency.

FIG. 24 is a block diagram illustrating a wireless apparatus toimplement the embodiments of the present invention.

Referring to FIG. 24, a wireless apparatus 2400 include a processor2410, a memory 2420, and a transceiver 2430. The transceiver 2430transmits and/or receives a wireless signal, and implements a physicallayer of IEEE 802.11. The processor 2410 may be functionally connectedto the transceiver 2430 to be operated. The processor 2410 may be set toimplement an STA grouping-based data transceiving method shown in FIGS.9 to 23.

The processor 2410 and/or the transceiver 2430 may include anApplication-Specific Integrated Circuit (ASIC), another chipset, a logiccircuit and/or a data processor. When an embodiment is implemented bysoftware, the above scheme may be implemented by a module (procedure,function and the like) to perform the above function. The module isstored in the memory 2420 and may be executed by the processor 2410. Thememory 2420 may be included inside the processor 2410. The memory 2420is separately located outside the processor 2410 and may be functionallyconnected to the processor 2410 by various means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

1-10. (canceled)
 11. A method for receiving data in a wireless local area network system, the method performed by a station (STA) operating in a power save mode comprising: receiving, from an access point (AP), a beacon frame including a Traffic Indication Map (TIM) element and a grouping parameter information element and determining whether there is a buffered frame for the STA based on the TIM element and the grouping parameter information element, wherein the grouping parameter information element includes a group ID field indicating a number of a plurality of STA groups, a group ID bitmap field indicating whether there is a buffered frame per STA group, and wherein the TIM element includes information indicating whether there is a buffered frame for STAs to which at least one of the plurality of STA groups belongs.
 12. The method of claim 11, wherein the grouping parameter information element further includes an association identifier (AID) field indicating a range of AIDs for each of the plurality of STA groups.
 13. The method of claim 11, wherein the group ID bitmap field includes a plurality of bits, each of the plurality of bits indicating whether there is a buffered frame for a corresponding one of the plurality of STA groups.
 14. The method of claim 11, further comprising: transmitting, to the AP, a power save-poll frame when it is determined that there is the buffered frame for the STA.
 15. The method of claim 11, further comprising: entering into a doze state when the TIM element does not include information about a STA group to which the STA belongs.
 16. A station (STA) for receiving data in a wireless local area network system, the station comprising: a transceiver configured to receive radio signals and a processor operatively coupled with the transceiver and configured to instruct the transceiver to receive, from an access point (AP), a beacon frame including a Traffic Indication Map (TIM) element and a grouping parameter information element and determine whether there is a buffered frame for the STA based on the TIM element and the grouping parameter information element, wherein the grouping parameter information element includes a group ID field indicating a number of a plurality of STA groups, a group ID bitmap field indicating whether there is a buffered frame per STA group, and wherein the TIM element includes information indicating whether there is a buffered frame for STAs to which at least one of the plurality of STA groups belongs.
 17. The STA of claim 16, wherein the grouping parameter information element further includes an association identifier (AID) field indicating a range of AIDs for each of the plurality of STA groups.
 18. The STA of claim 16, wherein the group ID bitmap field includes a plurality of bits, each of the plurality of bits indicating whether there is a buffered frame for a corresponding one of the plurality of STA groups. 